1. Field of the Invention
The present invention relates to a high-frequency signal line and a manufacturing method thereof, and more particularly to a high-frequency signal line preferably for use in high-frequency signal transmission and a manufacturing method thereof.
2. Description of the Related Art
As a conventional high-frequency signal line, for example, a high-frequency signal line disclosed in WO 2012/073591 is known. The high-frequency signal line includes a dielectric body, a signal line and two ground conductors. The dielectric body is a laminate of dielectric sheets formed of a flexible material, and extends in a predetermined direction. The signal line is a linear conductor provided on one of the dielectric sheets. The two ground conductors are provided on any of the dielectric sheets so as to sandwich the signal line in the direction of lamination. Accordingly, the signal line and the two ground conductors form a stripline structure. The high-frequency signal line is used, for example, in an electronic device to connect two circuit boards.
The high-frequency signal line disclosed in WO 2012/073591 is bent when used in an electronic device. To this end, the dielectric body of the high-frequency signal line is flexible. However, since the whole high-frequency signal line is flexible, even a portion supposed to extend straight without bending may bend. In this case, in the bending portion of the high-frequency signal line, the interval between the signal line and each of the ground conductors becomes smaller, and it is likely that greater capacitance is created between the signal line and each of the ground conductors. Accordingly, the characteristic impedance in the bending portion of the high-frequency signal line becomes lower than the characteristic impedance before bending. Thus, there is a risk in the high-frequency signal line disclosed in WO 2012/073591 that the characteristic impedance shifts from a designed value (for example, 50Ω).